\begin{tikzpicture}[>=Stealth, scale=0.6,
    every node/.style={inner sep=1pt},
]
    \draw [->] (-4, 0) -- (4.5, 0) node[below=0.2em] {$x$};
    \draw [->] (0, -2) -- (0, 4.5) node[left=0.2em] {$y$};
    \draw (0, 0) node [above left] {\small $O$};

    \coordinate (A) at (-1, 2.5);
    \coordinate (B) at (2, 0);
    \coordinate (C) at (-2, 0);
    \pgfmathsetmacro{\r}{0.7}
    \pgfmathsetmacro{\R}{1.5}

    \filldraw [fill=black] (A) circle (0.05);
    \filldraw [fill=black] (B) circle (0.05);
    \filldraw [fill=black] (C) circle (0.05);

    \draw [thick] (A) node [below right] {\small $A$} circle (\r);
    \draw [thick] (B) node [below right] {\small $B$} circle (\r);
    \draw [thick] (C) node [below right] {\small $C$} circle (\r);

    \path (A) +(30:\R)  coordinate(pa);
    \path (C) +(150:\R) coordinate(pc);
    \path (B) +(270:\R) coordinate(pb);

    \draw [rounded corners] (pa)
        arc [radius=\R, start angle=30,  end angle=150]
        to [bend left] (pc)
        arc [radius=\R, start angle=150, end angle=270]
        to [bend left] (pb)
        arc [radius=\R, start angle=270, end angle=390]
        to [bend left] (pa);
\end{tikzpicture}

